Wireless networks have become ubiquitous. A wireless network refers to any type of computer network that is wireless, and is commonly associated with a telecommunications network whose interconnections between nodes is implemented without the use of wires.
A typical Wireless Local Area Network (WLAN) includes a Wireless Controller (WC), one or more Access Points (APs), one or more Mobility Switches (MSs) and one or more Mobility Units (MUs). A Mobility Domain (MD) is a single geographic area where a same set of mobility services are provided. A mobility domain can include tens of Wireless controllers, hundreds of MSs, thousands of APs, and tens of thousands of MUs. MUs can include laptops, cell phones, Personal Digital Assistants (PDAs) and the like.
A wireless AP is a device that allows wireless communication devices to connect to a wireless network. The mobility switches allow mobility units (e.g. laptops, cell phones etc.) to roam among various locations and still have network access. The mobile unit includes a wireless transceiver which can communicate with an access point. The communication can occur via radio waves, infrared, or any other known form of wireless communication. The access point allows wireless mobile units to communicate with each other and to communicate with infrastructure connected to the access point.
Wireless Local Area Networks (LANs) are a popular and inexpensive way to allow multiple users of “mobile units” (MUs) to communicate with each other, to access a wired LAN, to access a local server, to access a remote server, such as over the Internet, etc. A wireless local area network (WLAN) typically includes an Access Point (AP) and one or more mobile units. A wireless local area network may also include one or more Virtual Local Area Networks (VLANs). A VLAN includes a group of devices with a common set of requirements that communicate as if they were attached to the same broadcast domain, regardless of their physical location. A VLAN has the same attributes as a physical LAN, but allows for devices to be grouped together even if they are not located on the same network switch.
The server can provide services, such as access to applications like an email system, a word processing program, an accounting system and/or a dedicated database. Wireless LANs are employed within such facilities as businesses, university classrooms or buildings, airport lounges, hotel meeting rooms, etc. When a user is physically located in the vicinity of an access point, the transceiver of the mobile unit communicates with the access point and a connection to the wireless LAN is established.
APs and mobile units transmit data in units referred to as frames over a shared-communications channel. Frames transmitted from a mobile unit to an AP are referred to as uplink frames, and frames transmitted from an AP to a mobile unit are referred to as downlink frames. In a situation where two or more mobile units (or an AP and a mobile unit) transmit frames simultaneously, then one or more of the frames can become corrupted, referred to as a collision. As a result, Wireless Local Area Networks (WLANs) typically employ one or more protocols to ensure that a mobile unit or AP can gain exclusive access to the shared-communications channel for a predetermined interval of time in order to transmit its frames without collisions occurring.
Certain wireless network protocols (e.g., Institute of Electrical and Electronics Engineers [IEEE] 802.11, etc.) provide for the AP to periodically broadcast a special frame called a beacon that can be heard by the mobile units in the BSA (basic service area), the area covered by the AP. The beacon contains a variety of information that enables the mobile units to establish and maintain communications in an orderly fashion, such as a timestamp, which enables mobile units to synchronize their local clocks, and signaling information (e.g., channel number, frequency hopping pattern, dwell time, etc.).